According to prior art processes, natural optically active Vitamin E which is the 2R,4'R,8'R isomer of .alpha.-tocopherol, is manufactured from a known aldehyde of the formula: ##STR1## wherein R.sub.x is lower alkyl, lower alkanoyl or benzyl.
The prior art process for producing this aldehyde, however, presents many problems. For example, an acid firstly obtained in the manufacture of the above aldehyde is always produced in racemic form and can be separated into its optical antipodes only in an extremely complicated manner. Further, the undesired antipode of the acid cannot be racemized and restored into the process which accordingly leads to considerable material loss.
We have invented an improved process for producing the aldehyde of formula I via optically active intermediates which avoids the difficulties of the prior art.